Some of the most obvious differences between normal and cancer cells, such as loss of growth control and increased agglutinability, are highly correlated with changes in membrane organization. Thus we (R.D. Berlin, J.M. Oliver, H.H. Yin and T.E. Ukena) have approached the problem of understanding and control of neoplastic transformation by studying the processes that regulate cell surface topography. We have evidence from extensive studies with the colchicine and Vinca alkaloids, compounds that disrupt microtubules in plant and animal cells, that microtubules are intimately involved in regulating membrane organization and function in mammalian cells. Another class of compounds, the carbamate herbicides (isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl) carbamate (CIPC) have been shown to inhibit plant growth by disruption of microtubules. Cytoplasmic and membrane-associated microtubules are highly sensitive to IPC and CIPC and mitotic spindle microtubules show lower sensitivity. In contrast the colchicine and Vinca alkaloids affect all populations of microtubules. The action of the carbamate herbicides in mammalian cells has not been studied in detail. However our preliminary experiments showed inhibition of growth of cultured fibroblasts at low drug concentrations. In addition they alter certain surface properties of leucocytes in a similar manner to colchicine. This indicates that mammalian microtubules may also be disrupted by the carbamate herbicides. These compounds offer a unique tool for studies of the role of specific populations of microtubules in the control of membrane organization and of surface properties that change during neoplastic transformation. In addition, analysis of their effects on mammalian microtubule structure and function will show whether or not these compounds like colchicine are likely to be toxic to animals and so unsuitable for use as herbicides.